1) Field of the Invention
The present invention relates to a pedestrian collision protection system for a vehicle, and to a collision site (position) detecting apparatus suitable for use in the pedestrian collision protection system.
2) Description of the Related Art
So far, there has been proposed a pedestrian collision protection apparatus for a vehicle in which a pedestrian collision detecting apparatus (which will hereinafter be referred to equally as a xe2x80x9cbumper sensorxe2x80x9d) is placed on a front bumper of a vehicle to detect a collision with a pedestrian so that, if this detecting apparatus has detected a collision of the vehicle with a pedestrian when the vehicle is in a traveling condition, an air bag provided at an upper surface of a front portion of the vehicle, or the like, is activated to alleviate the impact to be made on the pedestrian who collapses onto the upper surface of the front portion of the vehicle.
As one example of the pedestrian collision protection system, Japanese Patent No. 3212841 discloses a technique in which, in addition to the aforesaid bumper sensor (collision detecting element), a laser light emitting/receiving device (collision site detecting element) is provided to monitor a space above a front portion of a vehicle and an upper surface of the vehicle front portion is divided into a plurality of areas and an air bag (pedestrian protecting element) is provided in each of the areas.
The laser light emitting/receiving device is made to emit laser beams from right and left sides of a front portion of a vehicle toward a pedestrian collapsing onto the space above the vehicle front portion to, on the basis of reflected light therefrom, make a decision as to whether the pedestrian falls into the right side or left side of the upper surface of the vehicle front portion. This enables only an air bag in the falling-into-side to be spread, thus achieving the size reduction of the air bag.
The concrete examples of the bumper sensor (collision detecting element) are disclosed in Japanese Patent Laid-Open Nos. HEI 8-216826 and HEI 11-310095. The bumper sensor disclosed in the former document is constructed in a manner such that electrodes are placed on both sides of an electric conductive rubber containing a metallic conductive fine-grain and is formed into an elongated configuration to securely detect a collision of a pedestrian even where the pedestrian collides in a front bumper. The bumper sensor disclosed in the latter document includes a pressure sensor for sensing an internal pressure of an elastic tube filled with a gas and is made to detect a collision against a pedestrian on the basis of a rise of the internal pressure of the elastic tube.
The pedestrian collision protection system disclosed in Japanese Patent No. 3212841 is capable of making a decision on a site (position in right- and left-hand directions) of a collision against a pedestrian and, hence, enables the size reduction of an air bag to be spread. In consequence, it is possible to quickly operate an impact buffering device, such as spreading an air bag, with a less application force, which is advantageous in practical use.
However, this pedestrian collision protection system can detect a collision itself through the use of the bumper sensor but creating problems in that 1) difficulty is encountered in making a decision on a collision site with a pedestrian until one of or both the right- and left-side laser light emitting/receiving devices for the pedestrian collision site detection detects the pedestrian falling into a space above a front portion of the vehicle and, hence, the time from when the collision site is confirmed until the spreading of an air bag becomes short, 2) if intensive sunlight is incident on the light-receiving portion of the laser light emitting/receiving device, the incident light quantity exceeds its input dynamic range to make it difficult to detect a pedestrian forming an object of optical reflection, 3) the equipment cost becomes high because a pair of laser light emitting/receiving devices are required for monitoring the object of optical reflection above the vehicle front portion, and 4) the detection accuracy drops due to dirt and damage to lens surfaces. For these reasons, it is difficult to put it in practical use.
The bumper sensor disclosed in Japanese Paten Laid-Open No. HEI 8-216826 has a structure in which an electric conductive rubber containing a metallic conductive fine-grain is interposed between a pair of electrodes and is made to detect a collision against a pedestrian through the use of the phenomenon in which the electric resistance value between both the electrodes lowers when the electric conductive rubber is compressed by the collision. However, since there is a need for the bumper sensor to detect a collision against a pedestrian irrespective of the collision position in lateral directions of the vehicle, the total electrode area becomes naturally large. Meanwhile, in the case of such a conductive grain dispersed rubber, difficulty is encountered in easily reducing the direct-current leakage at non-collision. Considering the large electrode area, the direct-current loss becomes considerably large.
Moreover, in the case of the bumper sensor disclosed in Japanese Paten Laid-Open No. HEI 11-310095, difficulty is experienced in maintaining the internal pressure of the elastic tube, and a delay in activation of an air bag occurs due to a delay in detection stemming from a pressure propagation time in the interior of the tube.
Accordingly, the conventional pedestrian collision protection systems require, in addition to the bumper sensor (a sensor fixedly secured onto a front bumper) for detecting a collision against a pedestrian to recognize a collision site in right- and left-hand directions (lateral directions) of a vehicle, the additional use of a sensor for specifying the collision site in the lateral directions and, hence, there is a need to considerably reduce the manufacturing cost and solve the detection delay problem.
Meanwhile, in the case of conventional collision detecting apparatus, even if the detection of a collision is feasible, difficulty is encountered in distinguishing between a pedestrian and an object of collision other than the pedestrian. In order to avoid useless activation of a pedestrian protecting device such as an air bag, it is preferable to activate the pedestrian protecting device after the confirmation that the object of collision is a pedestrian.
As methods of making a decision as to whether an object of collision is a pedestrian, there have been known techniques proposed in Japanese Patent Laid-Open Nos. HEI 11-028994 and HEI 11-310095. Japanese Patent Laid-Open No. HEI 11-028994 discloses the technique using a collision load (or deformation quantity), a duration thereof and a vehicle speed, while Japanese Patent Laid-Open No. HEI 11-310095 discloses the technique using a deformation quantity at a collision, its variation with time and a vehicle speed.
That is, these decision technique utilize the phenomenon in which, when a collision against a pedestrian occurs, a leg portion of the pedestrian is thrown up or dashed off after the collision. Concretely, a leg portion thereof departs from a bumper after the collision and, for this reason, the magnitude of a load or deformation quantity, to be detected by a sensor, attenuates after the collision against the vehicle. A decision on a pedestrian is made through the use of this phenomenon.
However, the pedestrian decision techniques disclosed in these documents encounter a problem in that the time for which a collision load or a deformation quantity exceeds a threshold (which will hereinafter be referred to as equally to a xe2x80x9ccollision detection durationxe2x80x9d) varies diversely in accordance with a state of a leg portion of a pedestrian.
That is, in a case in which a vehicle speed is approximately 40 km/h, the time from which only one leg collides against a bumper until it is thrown up, or the time until both legs are thrown up by a bumper when both legs of a pedestrian are in place (are put in order) in a vehicle advancing direction, are approximately 10 to 20 ms. In the latter case, since the leg portion first thrown up by the bumper biases the other leg portion adjacent thereto, the collision detection duration does not show a large difference from that in the case in which only one leg colliding against the bumper.
However, in most cases of collision against a pedestrian, both leg portions of the pedestrian are not in place with respect to a bumper, and the distance between on leg portion and the bumper and the distance between the other leg portion and the bumper provide a difference which affects the aforesaid collision detection duration and, in consequence, in this case, the time from which both leg portions are thrown up until a collision load or a deformation quantity falls below a threshold (that is, the end of the collision detection duration) becomes considerably longer as compared with the case in which only one leg portion or both leg portions being in place in a vehicle advancing direction are thrown up. That is, the time needed for the pedestrian decision is prolonged and the time taken for the apparatus operation becomes shorter, which makes the apparatus operation difficult.
The present invention has been developed with a view to eliminating the above-mentioned problems, and it is therefore an object of the present invention to provide a pedestrian collision protection system for a vehicle and collision site detecting apparatus suitable for use in the pedestrian collision protection system, which can provide easy manufacturing and can quickly specify the pedestrian collision side in the lateral directions.
For this purpose, in accordance with an aspect of the present invention, there is provided a pedestrian collision protection system for a vehicle, comprising a collision detecting element fixedly secured to a bumper of a vehicle for detecting a collision against a pedestrian, a collision site detecting element for detecting a position of a collision site in lateral directions, and a pedestrian protecting element provided in the vehicle for protecting the pedestrian from the collision according to the pedestrian collision site in the lateral directions at the collision against the pedestrian on the basis of outputs of the pedestrian collision detecting element and the pedestrian collision site detecting element, wherein the collision detecting element also functions as the collision site detecting element and includes a line sensor composed of a plurality of conductive lines which are separated from each other by a predetermined spacing to confront each other and come into contact with each other when the collision against the pedestrian occurs, and a detection circuit unit made to detect the collision detection and the collision site detection on the basis of a variation of electric energy (quantity of electricity) related to an impedance between the plurality of conductive lines.
In this pedestrian collision protection system for a vehicle, when a pedestrian collides with the line sensor disposed in longitudinal directions of the bumper, the plurality of conductive lines constituting the line sensor are locally deformed to come into contact with each other. Therefore, the detection of the occurrence of a collision against a pedestrian and the specification of the pedestrian collision site are accomplished by making a decision as to the resultant impedance variation between the conductive lines.
This can considerably simplify the system configuration as compared with such conventional systems and achieve the size and weight reduction of a portion of the pedestrian protecting element, operating in response to a collision, while preventing the delay in activation or operation of the pedestrian protecting element by specifying a pedestrian collision site.
Incidentally, the aforesaid contact is sufficient if it causes a detectable impedance variation between the conductive lines, and for the impedance variation, for example, a direct-current voltage or an alternating-current voltage may be applied through a resistive element for detection of a voltage drop to between the conductive lines to detect a voltage drop across the voltage drop detection resistive element.
In a preferred mode, the aforesaid line sensor includes a plurality of pairs of conductive lines successively arranged in a longitudinal direction of the bumper to detect the collision with the pedestrian independently of each other, and the detection circuit unit makes a decision indicative of the occurrence of the collision when detecting that at least two conductive lines constituting the conductive line pair are brought into contact with each other due to the collision, and makes a decision on the collision site on the basis of the location of the contact-made conductive line pair which have come into contact with each other.
This simple construction that involves locating the conductive lines at different positions in lateral directions of the vehicle can easily and accurately achieve the collision detection and the collision site detection simultaneously.
In a preferred mode, the aforesaid line sensor includes a pair of conductive lines placed to extend in a longitudinal direction of the bumper and confront each other in a state separated from each other by a predetermined spacing and made to come locally into contact with each other at a position of the collision with the pedestrian and its vicinities (a region near the collision position), and at least one of the conductive lines constituting the conductive line pair includes a resistive (resistor) line having a resistivity (specific resistance) in a numerical range which allows the detection of the current or voltage drop according to the occurrence or non-occurrence of the contact therebetween, and the detection circuit unit detects the collision and the collision site in the lateral directions on the basis of the current flowing in the conductive line pair or the voltage drop in the conductive line pair.
Thus, at least a pair of conductive lines are short-circuited (brought into contact with each other) at a collision site and, hence, the impedance varies between the conductive lines when viewed from a given portion of these conductive lines, for example, end portions thereof. This can realize the detection of the collision and the collision site in the lateral directions through the use of a small number of conductive lines.
In a preferred mode, the conductive line pair is composed of an electrode line made of a high-conductivity material and a resistive line made of a resistive material having a predetermined resistivity.
This permits the employment of a low-priced material, such as an aluminum plate or an aluminum film, for a portion of the conductive line, thereby leading to the reduction of the manufacturing cost.
In a preferred mode, the line sensor is fixedly secured to a portion of the bumper which protrudes most on an outside surface of the bumper.
This enables a high-sensitivity detection of the contact with a pedestrian, for that the pedestrian first comes into contact with the line sensor. In this connection, since the line sensor can be deformed together with the bumper, it is also possible that the line sensor is put in a groove made in the bumper or that the line sensor is formed integrally with the bumper.
In a preferred mode, the line sensor is fixedly secured to an inside surface of the bumper.
This enables the line sensor to be covered with the bumper, thus avoiding damaging the beauties.
In a preferred mode, one of the conductive lines is held by the other conductive line or the bumper in a state where an elastic member having an electrical insulating property is interposed therebetween.
This enables the conductive line to be easily restored to the original position after the detection of a collision.
In a preferred mode, one of the conductive lines has an elasticity whereby the conductive line is restorable to the original position and is locally deformed by the collision, and is held by the other conductive line or the bumper.
This can eliminate the need for the employment of the above-mentioned elastic member, thus leading to simplifying the manufacturing process.
In a preferred mode, a power supply source applies a supply voltage through a voltage drop detection resistive element to between the same-side end portions of the pair of conductive lines constituting the conductive line pair, and the detection circuit unit carries out the detection of the occurrence of the collision and the specification of the collision site on the basis of a voltage drop across the voltage drop detection resistive element.
This enables the high-sensitivity detection of the collision site.
In a preferred mode, the electrode line is connected to a first predetermined electric potential source and both ends of the resistive line are connected through different voltage drop detection resistive elements to a second predetermined electric potential source, and the detection circuit unit makes a decision on the collision site on the basis of voltage drops across the voltage drop detection resistive elements.
In this case, since the voltage of the electrode line is generally ignorable, the first voltage drop detection resistive element can secure a high detection sensitivity at one end side of the conductive line pair and the second voltage drop detection resistive element can secure a high detection sensitivity at the other end side of the conductive line pair. Thus, a high detection sensitivity providing a high linearity is obtainable at both end portions in the lateral directions with which a pedestrian tends to come into contact in such a manner as to detect the difference in voltage drop between both the voltage drop detection resistive elements.
In addition, in accordance with another aspect of the present invention, there is provided a collision position detecting apparatus suitable for use in the aforesaid pedestrian collision protection system, comprising a line sensor including at least two conductive lines fixedly secured to a front surface or rear surface of a vehicle and placed to extend in lateral directions of the vehicle in a state separated from each other by a predetermined spacing, and a detection circuit unit for detecting an electric energy related to an impedance between the predetermined positions of both the conductive lines, wherein at least one of both the conductive lines is made of a resistive material having a predetermined resistivity, and when a collision occurs, the spacing between both the conductive lines is locally elastically reduced at a position of the collision and its vicinities so as to be restorable, and the impedance varies according to the collision position.
That is, in this collision position detecting apparatus, at least two conductive lines, one of which has an electrical resistance to provide a resistive line, are provided on a front surface or rear surface of a vehicle to extend in lateral directions of the vehicle, and when a collision against a person or a collision against a thing occurs, the spacing between both the conductive lines is locally shortened so that they are brought into contact with each other. This enable the impedance between both the conductive lines viewed from predetermined positions of both the conductive lines to vary in accordance with a variation of the collision site. The impedance variation is easily detectable through the use of a well-known technique using a current variation, voltage variation, oscillating frequency variation, or the like, which permits the detection of a collision site through the use of a simple apparatus configuration and, simultaneously, the detection of the occurrence of a collision. If the collision site is quickly detectable at the occurrence of a collision, optimum collision-handling processing is achievable, such as spreading only suitable one of a plurality of air bags for the pedestrian protection placed in the exterior of the vehicle. This is advantageous in safety. Incidentally, as a substitute for a conductive line having no electrical resistance, i.e., an electrode line, it is also possible to use a vehicle body.
In a preferred mode, an alternating-current voltage and a direct-current voltage are applied to the line sensor, and the detection circuit unit makes at least the collision detection and the collision site detection on the basis of a variation of electric energy related to a direct current component flowing in the line sensor and detects approach of an obstacle on the basis of a variation of electric energy related to an alternating current component flowing in the line sensor.
In this case, as the direct-current voltage, any voltage is employable provided that it is separable in frequency with respect to the alternating-current voltage. For example, as the direct-current voltage, it is also possible to use an alternating-current voltage having a frequency lower than that of the aforesaid alternating-current voltage.
When a pedestrian, considered virtually as a large-capacity conductor or a capacitor whose one end is substantially grounded, approaches the conductive lines of the line sensor, an alternating-current component flows from the conductive lines toward the pedestrian side. Therefore, a signal representative of a collision-unavoidable condition is detectable prior to a collision against the pedestrian. Following this, if the collision occurs, the collision detection and the collision site detection are carried out as mentioned above. Accordingly, proper countermeasures can be taken prior to the collision.
Moreover, in a case in which a pedestrian or the like is considered as a capacitor having one end substantially installed, when a pedestrian approaches a predetermined position of a resistive line, the alternating-current impedance of the line sensor varies, and a real value (resistance) component and an imaginary value (capacity) component, constituting the alternating-current impedance, can easily be separated from each other. Therefore, it is also possible to estimate a collision site on the basis of a variation of the real value (resistance) component prior to the actual occurrence of the collision.
Furthermore, in accordance with a further aspect of the present invention, there is provided a collision position detecting apparatus for a vehicle, comprising a line sensor including first and second conductive lines fixedly secured onto a front surface or rear surface of the vehicle to extend in lateral directions of the vehicle and placed to be separated from each other by a predetermined spacing in longitudinal directions of the vehicle, with at least one of the conductive lines being elastically deformed at a position of a collision against a body to be restorable to make an electrical connection with the other conductive line, a power supply source for applying a voltage to a predetermined position of the first conductive line, a pair of voltage drop detection resistive elements individually connected between both end portions of the second conductive line and a predetermined constant-potential source, and a collision position detection circuit unit for discriminating a collision position obtained on the basis of voltage drops across both the resistive elements through the use of an n-bit digital signal, wherein, when an electrical resistance value per unit distance of the first conductive line in the lateral directions is taken as R1, an electrical resistance value per unit distance of the second conductive line in the lateral directions is taken as R2, an electrical resistance value of both the resistive elements is taken as R3, R3/R1 is expressed as S, a constant (required resolution/sensor installation width) is taken as dx, and a maximum allowable resistance ratio is taken as T, a resistance ratio (R2/R1) is set to be below T given by the following equation (1).                                           0             less than                           R2              R1                         less than                                                             (                                                            d                      ⁢                                              xe2x80x83                                            ⁢                      x                                        +                    S                                    )                                ⁢                                  {                                                                                    2                        n                                            ⁢                      d                      ⁢                                              xe2x80x83                                            ⁢                      x                      ⁢                                              xe2x80x83                                            ⁢                      S                                        -                                          (                                              1                        -                                                  d                          ⁢                                                      xe2x80x83                                                    ⁢                          x                                                                    )                                        -                                          2                      ⁢                                              xe2x80x83                                            ⁢                      S                                        -                                          S                      2                                                        }                                                                              (                                      1                    +                                                                  2                        n                                            ⁢                      S                                                        )                                ⁢                                  (                                      1                    +                                          2                      ⁢                      S                                                        )                                ⁢                                  xe2x80x83                                ⁢                d                ⁢                                  xe2x80x83                                ⁢                x                                              =          T                ⁢                  
                ⁢                  xe2x80x83                ⁢                  S          =                      R3            R1                                              (        1        )            
where dx: required resolution/sensor installation width
n: voltage read resolution multiplier (number of bits)
That is, when a pedestrian collides against a line sensor comprising a pair of conductive lines disposed in longitudinal directions of a bumper, the conductive lines are elastically deformed to come into contact with each other, and the collision position is detected on the basis of a variation of the electrical resistances of the conductive lines. In more details, a constant voltage is applied to one end of the first conductive line while both the ends of the second conductive line are grounded through resistive elements so that the collision position is detected on the basis of the voltage drops of the resistive elements at the collision. For example, in a case in which this vehicle collision position detecting apparatus is employed for a pedestrian collision decision, in the case of a collision with a pedestrian, if one leg of the pedestrian is thrown up while the other leg remains in a colliding condition, the collision position varies. Therefore, the pedestrian collision decision can be made by the detection of this collision position variation.
In a line sensor made to detect a collision position on the basis of a voltage drop of a resistive element, when an electrical resistance from a collision position of a conductive line to an end portion thereof is taken as R1, an electrical resistance of a resistive element connected to this end portion is taken as RC, a power supply voltage is taken as V, a unit distance variation in collision position is taken as xcex94X and a variation of a voltage drop V1 for the unit distance variation is taken as xcex94V1, a voltage drop V1 across the resistive element is given by V1=(RC/(RC+R1))V, and a voltage drop variation xcex94V1/xcex94X per unit distance variation in collision position becomes large at a central portion of the conductive line in lateral directions of a vehicle but becoming small at both end portions in the lateral directions, thus degrading the detection accuracy.
For this reason, according to the present invention, the resistance ratio (R2/R1) of the conductive lines is set to be below the value given by the aforesaid equation (1). This enables a variation xcex94V1/xcex94X of the voltage drop per unit distance variation in collision position to be maintained at over a value needed for the required resolution and enables the detection accuracy to be maintained at a required level even at both the end portions of the conductive line in the lateral directions.
In a preferred mode, when a contact resistance of both the conductive lines at a collision is taken as Rc and Rc/R1 is expressed as C, a resistance ratio (R2/R1) of the conductive lines is set to be below Txe2x80x2 given by the following equation (2). This can secure a required detection level even if the contact resistance thereof is high.       0     less than           R2      R1         less than                             F          ⁡                      (            S            )                          +                  G          ⁡                      (            S            )                                      H        ⁡                  (          S          )                      =      T    xe2x80x2  xe2x80x83F(S)=2nS[(dx+S){(1+S)S+(1+2S)C}xe2x88x92S{(dx+S) (1xe2x88x92dx+S)+(1+2S)C}]
G(S)=xe2x88x92{S(1+S)+C(1+2S)}{(dx+S)(1xe2x88x92dx+S)+(1+2S)C}
H(S)={S(1+2nS)+C(1+2S)}(1+2S)dx
                                                        S              =                              R3                R1                                                                                        C              =                              Rc                R1                                                                        (        2        )            
where dx: required resolution/sensor installation width
n: voltage read resolution multiplier (number of bits)
In addition, in accordance with a further aspect of the present invention, there is provided a pedestrian collision detecting apparatus for a vehicle, comprising a line sensor including first and second conductive lines fixedly secured onto a front surface or rear surface of the vehicle to extend in lateral directions of the vehicle and placed to be separated from each other by a predetermined spacing in longitudinal directions of the vehicle, with at least one of the conductive lines being elastically deformed at a position of a collision against a body to be restorable to make an electrical connection with the other conductive line, a power supply source for applying a voltage to a predetermined position of the first conductive line, constant current circuit units individually connected between end portions of the second conductive line and a predetermined constant-potential source, and a collision position detection circuit unit for determining a collision position on the basis of voltage drops across the constant current circuit units.
This can make constant a variation xcex94V1/xcex94X of the voltage drop per unit distance variation in collision position at each parts in lengthwise directions of the conductive lines, thus providing high detection accuracy.
In a preferred mode, the collision position detection circuit unit detects the collision position on the basis of a difference in voltage drop between the pair of constant current circuit units individually placed between both the end portions of the second conductive line and the predetermined constant-potential source. This can eliminate the degradation of the detection accuracy stemming from a variation of the contact resistance of the pair of conductive lines, thus realizing satisfactory collision position detection accuracy.